The present invention is generally directed to the design and implementation of complex circuits to reduce distortion and linearize the output corresponding to radio frequency (RF) and microwave frequency ranges. An embodiment of the present integrated circuitry (IC) is configured to use a combination of Heterojunction Bipolar transistors (HBT) and resonant circuits to effectively provide linearization and dynamic power control for RF and microwave signals.
Today, one problem with operating a power amplifier at low distortion levels is that the efficiency of the amplifier circuit is greatly reduced because it is not amplifying at its highest capability. Therefore, a circuit according to the present system can preferably utilize a bias circuit to adjust the bias characteristics and subsequent power amplification corresponding to changing circuit conditions.
Specifically, the circuit may preferably utilize a leakage current of the RF input to determine the state of amplification and accordingly adjust the bias. By adjusting the bias conditions and power amplification characteristics to the existing conditions, power amplification efficiency is greatly improved.
Demands on the linearity and efficiency of power amplifiers are common in radio frequency and microwave communication systems. Conventionally, power amplifiers normally operate at maximum efficiency at or near saturation. However, in order to accommodate the linearity of today's devices with communication signals having varying amplitudes (e.g. cellular telephones), systems utilizing conventional power amplifiers normally operate at less than peak efficiency for a substantial portion of the time.
Of course, in today's market, wireless communications devices, such as cellular telephones, must consistently provide clear and undistorted transmissions. As well, the batteries in the devices must be small in physical size while maintaining a long operating life.
In order to meet these consumer requirements, wireless telephone designers and engineers have moved away from using traditional silicon-based bipolar transistors in power amplifiers and toward using more exotic transistors, such as heterojunction bipolar transistors (“HBTs”) made of aluminum-gallium-arsenide/gallium-arsenide (“AlGaAs/GaAs”) and indium-gallium-phosphide/gallium-arsenide (“InGaP/GaAs”). Such HBTs provide outstanding power efficiency and high linearity, thus enabling cellular phones to achieve longer battery life and better signal characteristics for voice and data.
Additionally, the trend in data networks is to provide higher data rates with complex modulation schemes. Complex modulation schemes require the design and implementation of linear systems in order for data transmission to be successful. In most cases, linear system design places significant constraints on individual circuits within the system.
Quite often the modulated signals applied to the system have very high peak-to-average-power-ratio (PAPR) which requires the individual circuits in the system to be designed so that they can withstand a large range of power levels. Essentially, the individual circuits must be designed with a large dynamic range, which makes the circuits inefficient and expensive.
Ultimately, circuit linearization techniques provide solutions to problems associated with signals requiring large dynamic ranges. Techniques that implement feedback, predistortion, feedforward, and other signal processing concepts are not feasible for use in RFIC designs. The technique used in the present embodiments allows for linearization and dynamic power control to be implemented in RFICs by manipulating aspects of the bias circuitry.
The present circuitry provides a linear amplifier configured with a bias circuit which is capable of realizing a high-efficiency operation during high output, while maintaining a linear operation.
Additional embodiments, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.